Objectives: 1) To evaluate diagnostic techniques for B. pertussis in relation to the stage of illness and to discern which techniques provide optimal recognition of B. pertussis infection. 2) To determine the reservoir of B. pertussis infection and to assess the significance of adult transmission to infants. 3) To better understand the serologic response to contact with B. pertussis, and to discern which antibodies are important for immunoprotection. To date, six index cases and 19 household contacts have been enrolled and evaluated. Nasopharyngeal specimens have been processed with routine culture medium and direct fluorescent assay. In addition, newly developed techniques have been used with the clinical specimens. These include mouse monoclonal antibodies, developed in the Laboratory of Pertussis, for the immunofluorescent assay, and serologic methods to detect pertussis-specific antibodies. On-going enrollment of index cases of pertussis and their contacts is planned to permit evaluation of the epidemiology of pertussis within a family and the community. Preliminary analyses have indicated that all of the confirmed index cases had elevated IgA antibody in saliva, suggesting that these responses could be useful in diagnosis. Although most exposed contacts had no or mild symptoms, it appears that most were infected because essentially all had elevated pertussis antibodies in serum and saliva.